Theme: 11. Advanced Diagnostic Tools

Topic Area: 11a. Environmental Forensics: Site Characterization and Source Determinations

Formatted Title:

Noble Gas Analyses to Distinguish between Surface and Subsurface Brine Releases at a Legacy Oil Site

Background/Objectives:

Attributing the sources of legacy contamination at oil and gas sites, including brines, is important to determine remediation options and to allocate responsibility. To make sound remediation decisions, it is necessary to distinguish subsurface sources, such as leaking oil and gas wells or natural upward fluid migrations, from surface releases. While chemical signatures of surface and subsurface releases may be similar, they are expected to imprint specific dissolved noble gas signatures, caused by accumulation of terrigenic noble gases in subsurface leaks or re-equilibration of noble gases following surface releases.

Approach/Activities:

We demonstrate that only a historical surface release influenced the dissolved noble gas signature of groundwater in monitoring wells contaminated with brine near an abandoned oil well, rather than subsurface leakage from the well. Elevated brine concentrations were associated with lower terrigenic helium concentrations, indicating re-equilibration with atmospheric helium at the surface during the release. Geophysical surveying indicating elevated salinity in surficial soils upgradient of the wells further supported the interpretation of the noble gas data.

Results/Lessons Learned:

Eliminating the possibility that subsurface leakage was the source of the plume was critical to selecting the proper remedial action at the site, which otherwise may have included an unnecessary and costly well re-abandonment. This is the first study demonstrating use of noble gas analysis to compare potential sources of brine contamination in groundwater and to exclude subsurface leakage as a potential source in an oilfield.

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